Impact Extrusion
Impact extrusion is a process by which products are made with a metal slug. The slug is pressed at a high velocity with extreme force into a die/mold by a punch.
Process
The punch is attached to a mechanical or hydraulic press. These machines reciprocate a cycle 20 to 60 times per minute. A cold slug is placed below the punch and over the die. The punch makes contact with the slug forcing it around the circumference of the punch and into the die. The metal slug deforms to fit the punch on the inside and the die on the outside. It only takes one impact for the finished shape to form from the slug. Once the slug has been contoured to the desired shape a counter-punch ejector removes the work piece from within the die.
Some Characteristics of the Process
The wall thickness of the work piece is directly correlated with the clearance between the punch and die.
The thinner the wall of the work piece the tighter its tolerances are.
The end product has a better surface finish than the starting piece.
Die Style
Three major types of dies (tools) can be used. They are: forward, backward/reverse, combined, and hydrostatic extrusion. Forward extrusion pushes the slug into the die. Backward/reverse extrusion pushes the slug around the punch. Combined extrusion forces the slug both into the die and around the punch. Hydrostatic extrusion is used on brittle materials (i.e. molybdenum, beryllium, and tungsten) by applying pressure gradually to force the brittle material through the die. This is generally accomplished by the same method as forward extrusion. (1)
Example products made from impact extrusion
Toothpaste tube, nozzle, aluminum beverage can, CO2 cartridge, ammunition casing (2).
References
1. Information and images provided. Manufacturing Processes Reference Guide. Industrial Press, 1st edition, 1994. Robert H. Todd, Dell K. Allen, and Leo Alting
2. http://www.cci-ammunition.com